Compare All Common Columns

Every common-column comparison must pass.

highlighted = computed this step

When two names are shared, both comparisons must pass.

\text{all common columns}

Read candidate checks

This example has 2 common columns and 3 matched rows.

\text{matches}=3

NATURAL JOIN examples are tiny finite-table transforms; SQL dialect completeness, type coercion, optimizer behavior, execution cost, indexing, output ordering guarantees, and database-product claims are out of scope.

One failed check drops the pair

A row pair needs every common-column check to say yes.

\text{AND over common columns}

Summary

NATURAL JOIN can be stricter than a one-key join when more names overlap.

\text{extra names matter}